This mind-bendingly important. In 1999, you could download one single installer on Windows, run it and with literally no further configuration you'd be writing PHP on an Apache/MySQL stack. No other environment even came close at the time and for a long time following.
This is still the main reason why I use PHP: the development cycle is just so fast, and if you are experienced enough to write good code without anyone holding your hand, you can do great work in PHP in a much shorter period of time when compared to most other platforms (at least the ones I've tried).
When people criticise the PHP language I think they really miss the point: it is the PHP platform that is really powerful because of:
1. The shared nothing architecture (it really helps you scale).
2. The rapid development cycle.
3. The portability (Apache, IIS, nginx, persistent in-memory interpreters via PHP-FPM...).
4. The huge amount of native C extensions providing amazing functionality.
Sure the language has warts, but who cares when the platform is this powerful?
As someone learning, I figured out pretty quickly from many forum threads about this topic, that I was simply too ignorant to be confident in writing solid PHP. I am in no rush to do anything useful (just having fun), and I'm trying to concurrently learn Vim and Git. so I chose Python. I might try PHP, if I ever feel I have learned to write OO code competently.
tl;dr: Too many gotchyas for a beginner. I need discipline imposed on me when I'm learning, ymmv.
Yep. And compared to Rails, something like mod_php is just so much faster and less resource hungry, it hurts. I use both regularly in production, and scaling the PHP side is almost trivial compared to the rails side.
Sorry to nitpick but that isn't scaling. Unless I can add double the number of machines and double or almost double the capability, and keep doing so to thousands of machine your application doesn't scale.
In the case of web applications all tend to scale equally well as you can just add another web server. Its the database that causes the scale issues.
Scaling vertically is still a valid strategy, and is scaling. Not every company needs to be able to scale to the moon, and if they don't, it's a poor use of time to focus too much on architecting for scalability.
With a lightweight PHP framework and a sensibly written app, you can stick to one machine for much longer than you can with Rails, and after that, it will require a fraction of the number of app servers. Beyond that, app processing time is generally much lower without all of that cruft, so you don't need to do as much caching, etc. to get a snappy webpage.
